Support returning async iterables from resolver functions

Author: robrichard

src/execution/__tests__/lists-test.ts

@@ -145,6 +145,25 @@ describe('Execute: Accepts async iterables as list value', () => {
     });
   });
 
+  it('Handles an AsyncGenerator function where an intermediate value triggers an error', async () => {
+    async function* listField() {
+      yield await Promise.resolve('two');
+      yield await Promise.resolve({});
+      yield await Promise.resolve(4);
+    }
+
+    expect(await complete({ listField })).to.deep.equal({
+      data: { listField: ['two', null, '4'] },
+      errors: [
+        {
+          message: 'String cannot represent value: {}',
+          locations: [{ line: 1, column: 3 }],
+          path: ['listField', 1],
+        },
+      ],
+    });
+  });
+
   it('Handles errors from `completeValue` in AsyncIterables', async () => {
     async function* listField() {
       yield await Promise.resolve('two');

src/execution/execute.ts

@@ -858,7 +858,6 @@ function completeAsyncIteratorValue(
             );
             handleFieldError(error, itemType, exeContext);
             resolve(completedResults);
-            return;
           }
 
           next(index + 1, completedResults);